X3 on Progressive Industries surge protector. They're getting the best review for customer service / lifetime warranty. I hard-wired mine before the power gets into the transfer switch. I went with the 50amp hard-wire unit but they also one that will plug into the power pole then you plug the coach into that (the long way of saying portable unit).
for downgrading to the camp amperage you just use a dog-bone at the pole (for whatever service you need) to your 50amp power cord. The surge protector still does it's job downstream.